1. Field of Invention
The invention relates to an operation control of an internal combustion engine in which the amount of intake air can be adjusted in at least two fashions based on the period during which an intake valve is open, and the degree of throttle opening.
2. Description of Related Art
In some internal combustion engines, electromagnetic valves are adopted as intake valves and exhaust valves so that the period of time during which these valves are open (hereinafter, referred to as “operation angle” that represents the open valve period of time in terms of the angle of a crankshaft), the amount of lift of the valves, and the phase thereof can be changed. In such engines, the amount of intake air can be controlled on the basis of two factors, that is, the intake valve operation angle and the degree of throttle opening.
Examples of the technology for controlling the amount of intake air based selectively on the operation angle and the degree of throttle opening are as follows. Japanese Patent Application Laid-open No. 2001-159355 discloses a technology in which the degree of throttle opening is used to control the amount of intake air in a low-load region whereas in a high-load region both the operation angle and the degree of throttle opening are used. Japanese Patent Application Laid-open No. 2001-221094 discloses a technology in which during idle engine operation, an intake amount control based on the operation angle and an intake amount control based on the degree of throttle opening are selectively performed, and during the switching period of transition between the two controls, a torque shock is reduced by a feedforward control.
However, according to the related-art technologies, a torque shock often occurs at the time of switch between the operation angle-based intake amount control and the throttle-based intake amount control or during execution of the operation angle-based intake amount control during a normal engine operation. Thus, the packaging of the intake amount control based on the valve operation angle still has room for improvement.